Pressure filter with a back-flushing head exerting a uniform contact pressure

ABSTRACT

A pressure filter having a fluid compartment with a fluid inlet, at least one filter surface in the fluid compartment having a plurality of apertures, one side of the filter surface being restricted by the fluid compartment and the other side thereof being restricted by a filtrate compartment and having a filtrate outlet, and a backwasher means. The backwasher means includes a backwashing head sweeping over the filter surface and sealing a part thereof with respect to the fluid compartment. It restricts a backwashing compartment having at least one suction chamber open in a slot-like manner to the filter surface and having connected thereto a reject drain. A resiliently acting pressure unit is associated with the slat-like or plate-like backwashing head, the pressure unit pressing the radial outer portion of the backwashing head axially towards the filter surface. By this, a uniform contact pressure of the backwashing head against the filter surface in radial direction is guaranteed.

SPECIFICATION CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national phase of PCT/DE 94/00704 filed June 1994and based, in turn, upon German National application P 43 20 952.1 underthe international convention.

FIELD OF THE INVENTION

The present invention directs to a pressure filter comprising a fluidcompartment with a fluid inlet, at least one filter surface within thefluid compartment having a plurality of apertures, one side of thefilter surface being restricted by the fluid compartment and the otherside thereof being restricted by a filtrate compartment having afiltrate outlet, and backwashing means with a slat-like or plate-likebackwashing head sweeping over the filter surface and sealing a part ofthe filter surface with respect to the fluid compartment, thebackwashing head having a backwashing compartment restricting at leastone suction chamber open in a slot-like manner to the filter surface,the backwashing compartment having a reject drain connected thereto.

BACKGROUND OF THE INVENTION

A pressure filter of the above-described type is known from EP 0 479 077A1. This pressure filter works with a continuous cleaning of the filtersurface and is especially destined for the separation of solids fromsuspensions. To the fundamental construction of such a pressure filter aplurality of pressure-tight filter elements separating the fluidcompartment from the filtrate compartment and forming the filter surfaceand the backwashing means connected to the reject drain and having abackwashing head sealing a part of the filter surface with respect tothe fluid compartment belong. The backwashing head and the filtersurface are movable with respect to one another. The fluid to befiltered is supplied to the pressure filter with a pressure P₁ and actson the filter elements with this pressure P₁ in the fluid compartment.The filtrate is drained from the filtrate compartement with a lowerpressure P₂. In the reject drain and backwashing compartment restrictedby the backwashing head a pressure P₃ is adjustable which is alwayssmaller than the pressure P₂ in the filtrate compartment. A filtrationoccurs on account of the pressure difference between the pressure P₁ ofthe fluid compartment and the pressure P₂ of the filtrate compartment,wherein solids are deposited on the filter surface and form a coverlayer. This cover layer is continuously cleaned by backwashing, i.e. aconversion of the flow direction through the filter elements. Thebackwashing occurs at that portion of the filter surface which is sealedby the backwashing head with respect to the fluid compartment with apressure difference between the pressure P₂ in the filtrate compartmentand the pressure P₃ in the backwashing compartment. The filtrationprocess at the remaining filter surface of the pressure filter is notinfluenced by the backwashing.

According to the known pressure filter the backwashing compartment hasat least one suction chamber open to the filter surface in a slot-likemanner. This suction chamber is formed as elongated chamber extendingfrom a central drive shaft for the backwashing head radially outwardly.Upon rotation of the backwashing head the slot-like aperture sweeps overthe filter surface as a radial beam emanating from the center of thepressure filter. Now, it became evident that difficulties result toassure at each radial point of the slat-like or plate-like backwashinghead the same pressure against the filter surface. So, on account of thecentral support of the backwashing head, the pressure is higher in thecentral range than in the radial outer range. Especially, it becameevident in practice that the radial outer end portions of the slat-likeor plate-like head tend to lift off from the filter surface so that thecorrect realization of the backwashing progress can no more beguaranteed.

OBJECT OF THE INVENTION TO PROVIDE A PRESSURE

It is the object of the invention to provide a pressure filter of thecited type according to which the uniform pressure of the backwashinghead is assured over the whole radial dimension of the same.

SUMMARY OF THE INVENTION

According to the invention this problem is solved by the feature that aresiliently acting pressure means is associated with the slat-like orplate-like backwashing head and presses the radial outer portion of thebackwashing head axially towards the filter surface.

By the pressure means provided according to the invention one succeedsin assuring uniform pressure relations of the backwashing head withrespect to the filter surface. By this, the backwashing process can becarried out with the desired pressure difference between pressure P₂ inthe filtrate compartment and the pressure P₃ in the backwashingcompartment without disturbances with regard to the maintenance of thedesired pressure difference result by lifting off of the backwashinghead from the filter surface in the radial outer portions of the same.Accordingly, the cover layer formed on the filter surface can becontinuously cleaned in an especially uniform manner since uniformpressure relations in radial direction are guaranteed. The radial outerportions of the backwashing head do no more lift off from the filtersurface.

According to an improvement of the invention the pressure applied by thepressure means is adjustable. By this, the pressure can be selected inresponse to the present conditions and can be adapted to respectiveconditions. If one recognizes that normally relative uniform pressurerelations in radial direction are present the pressure means is adjustedsuch that only a slight additional pressure is applied to the outerradial portions by this. If the radial outer portions of the backwashinghead show a strong tendency with regard to lifting off from the filtersurface a correspondingly high contact pressure is adjusted.

Of course, the normal contact pressure of the backwashing head ispredetermined by the central support of the same during the installationof the head. The pressure means provided according to the inventionguarantees that uniform pressure relations are present over the wholeradial dimension of the backwashing head, i.e. applies an additionalpressure to the radial outer portions of the backwashing head if thisshould be necessary. On the whole, by the pressure means providedaccording to the invention a strengthening of the correspondingbackwashing head is obtained with the effect that the parts of thebackwashing head contacting the filter surface slide uniformly on thesame.

According to a further embodiment of the invention the part of thebackwashing head contacting the filter surface is resiliently supported.By this, especially good results are obtained in cooperation with thepressure means provided according to the invention since unevennessescan be compensated by the additional resilient support of the contactpart or the contact parts of the backwashing head without failing toreach the aim of a uniform contact pressure over the whole radialdimension of the backwashing head. Even upon the occurrence ofunevennesses on the filter surface also the radial outer portions of thecontact part or of the contact parts can be pressed against the filtersurface well so that, on the whole, the desired uniform contact pressureeffect is obtained. Obviously, with "contact part" or "contact parts"that part or those parts of the backwashing head are meant whichsurround the slot-like backwashing aperture or corresponding aperturesand slide on the filter surface.

Preferably, the pressure means is formed by at least one biased springstrut centrally supported at the backwashing head and at the radial endportion thereof. One spring strut or a plurality of spring struts arepresent dependent on the design of the backwashing head as slat or inthe form of a plurality of slats or as plate so that, with the design asplate, all the radial outer circumferential zones are pressed.Accordingly, uniform contact pressure relations result also incircumferential direction. The spring strut can be supported at thebackwashing head or in the plane thereof radially outside. Whensupporting at the backwashing head, i.e. by means of the central planethereof, a longer lever arm results which reinforces the desired contactpressure effect. On the other side, for this the space requirement ishigher.

Preferably, the spring strut is radially inside and radially outsideonly clamped, i.e. not mounted at the backwashing head by means ofadditional fastening means. Preferably, the support radially inside isrealized by means of a part-spherical stud in a part-spherical bearingsocket. By this, a corresponding flexibility of the support is achieved.The bearing socket is conveniently located at the central bearing of thebackwashing head. If a plurality of spring struts is present, aplurality of such bearing sockets is disposed around the central bearingof the backwashing head.

According to the invention the spring strut itself is preferablydesigned such that it has a rod engaging into a cylinder containing atleast one spring and biased by the spring. For the adjustment of thepressure the spring can be replaced, or a plurality of springs can bedisposed which are adapted to the respective conditions. Preferably, cupsprings are used which act on a piston-like enlargement at the end ofthe rod which is sealingly guided in the cylinder.

An especially preferred embodiment of the inventive pressure filter ischaracterized by the feature that the backwashing head comprises acarrier plate at which at least one hollow slat sweeping over the filtersurface is disposed, the hollow slat having the slot-like aperture. Theresiliently acting pressure means resiliently presses the radial outerportion of the carrier plate towards the filter surface. Accordingly,with this embodiment the pressure means does not directly act on thehollow slat provided with the slot-like aperture but acts on the carrierplate thereof. Preferably, a plurality of spring struts are used whichare uniformly spaced around the periphery of the carrier plate. In orderto not impede the filter process the carrier plate has preferably radialrecesses which give it approximately the shape of a Geneva stop. Here,for example, two spring struts are associated with each arm of the stop.

Conveniently, at least one bracket is disposed at the radial outer edgeof the carrier plate. The pressure means is tensioned against thebracket. This kind of fixation of the pressure means (spring struts) atthe carrier plate has had favourable results.

Above an embodiment of the backwashing head was described according towhich the same has a slat-like or plate-like design, but in each caseextends freely radially outwardly from its central bearing in acantilevered manner and, apart from the contact points with the filtersurface, has no further support on the filter surface. However, with theembodiment described below the slat-like or plate-like backwashing headhas a bearing at its radial end portion sliding or rolling on the filterelement including the filter surface. The contact pressure of thisbearing is also reinforced or modulated by means of the resilientlyacting pressure means so that a corresponding effect as with thecantilevered slat or carrier plate results.

According to a preferred design of this embodiment the bearing has atleast one roller rolling on a raised ring of the filter element.Accordingly, the roller and the ring of the filter element form a fixedguide which prevents that the backwashing head is pressed against thefilter surface too strongly. Preferably, the contact pressure of theroller against the filter element is adjustable by means of furtheradjusting means in addition to the pressure means.

As already mentioned above, the pressure means provided according to theinvention preferably cooperates with a resiliently supported contactpart or a plurality of resiliently supported contact parts of thebackwashing head. A corresponding compensation of unevennesses isobtained by this resilient support. Preferably, this resilient supportof the part of the backwashing head contacting the filter surface isformed by a resiliently supported plate on the lower side of thebackwashing head. This plate-like contact member surrounds therespective slot-like aperture on the lower side of the backwashing headby means of which the backwashing process is carried out. By this, theplate adapts itself very exactly to the filter surface so that acorresponding sealing with respect to the fluid compartment is obtained.

According to a feature of the invention the plate is supported by asilicone bearing, preferably by a silicone bearing which is formed bysheathed silicone gel cushions. Conveniently, the plate is guided onboth sides and not fastened to the backwashing head so that--throughsupport by the opposite filter surface--a floating support of the plateresults which can thus completely fulfil its compensation function.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become morereadily apparent from the following description, reference being made tothe accompanying drawing in which:

FIG. 1 is a vertical section through an inventive pressure filter;

FIG. 2 is a view of the pressure filter of figure 1 with removed housingwall and partly removed backwashing head and filter elements;

FIG. 3 is a schematic section through the central bearing of thebackwashing head with presentation of the support of a spring strut;

FIG. 4 is a section through a part of the carrier plate of thebackwashing head provided with a hollow slat, the part showing anembodiment of the resilient support of the contact plate;

FIG. 5 is a section through a part of a carrier plate with hollow slatwhich shows a further embodiment of the resilient support of a contactplate; and

FIG. 6 is a part-longitudinal section of the end portion of a carrierplate which is provided with a roller bearing.

SPECIFIC DESCRIPTION

The pressure filter shown in FIGS. 1 and 2 has a carrier ring 1 at theinner side of which support rings 15 and ribs 29 are connected in such amanner that a hub 23 is centrally held. The carrier ring 1 is closed atits two open sides by a respective circular filter element 12 which iscomprised of a first and a second perforated plate 13 between which asuitable filter fleece consisting of textile material is located. Thesefilter elements form a filter surface, respectively. The annularassembly consisting of the carrier ring 1 and the two filter elements 12is located within a housing 3 which forms a fluid chamber 21 which issupplied with the fluid to be filtered by means of an inlet 18. Afiltrate chamber having connected thereto a filtrate outlet line 19 islocated within the annular assembly of the carrier ring 1 and the filterelements 12.

A hollow shaft 9 open at both ends extends through the hub 23. It isguided through slide bearings, ball bearings and seals which preventthat fluid can enter the region of the hollow shaft. Connection piecesare mounted into the open ends of the hollow shaft 9 and rotate togetherwith the hollow shaft. A carrier plate 5 is mounted to this flange-likeenlarging connection piece in a rotatably fixed manner, respectively, asdescribed later on in detail.

The interior of the hollow shaft is connected to a ventilation line 17and to a reject drain 25. Both lines extend through the filtrate chamberand are provided with shut-off valves (shown at 20) outside of thepressure filter, respectively. A ventilation line 16 having a suitableshut-off valve extends also from the filtrate chamber to the outside ofthe pressure filter.

The annular assembly of the carrier ring 1, the two filter elements 12and the support rings 15 and the ribs 29 and the corresponding lines 16,17, 19, 25 are stationary within the housing 3.

The pressure filter has two backwashing heads of which each isassociated with a filter element 12 and sweeps over the filter surfacethereof. The backwashing heads consist of a carrier plate 5 and aplurality of helically curved backwashing slats 8 which are mounted atthe carrier plate. The design of the backwashing slats 8 is shown inFIG. 2. There, the drain part 7 of the backwashing slats located abovethe carrier plate 5 is shown. The carrier plate 5 has recesses betweenthe individual backwashing slats 8 so that fluid from the fluid chamber21 can enter the filtrate chamber through the filter surfaces. In theirinterior the backwashing slats 8 include suction chambers and areprovided with a helically curved slot-like aperture at their sideadjacent to the filter surface, by means of which the backwashingprocess is carried out. The substance formed as cover layer on thefilter surface is sucked off by means of the helical slot-like apertureand is passed to the reject drain part 7 of the backwashing slatsthrough apertures formed in the carrier plate 5. From the reject drainpart the reject moves radially inwardly into the hollow shaft 9 and fromthere to the reject drain 25 to the outside of the pressure filter.

The backwashing heads are driven by the hollow shaft 9 which isconnected on its outside to a cup gear which meshes with a bevel gear ofa drive shaft 10 disposed within a tube 24 extending through the fluidchamber and the filtrate chamber. The drive shaft 10 is rotated by meansof a suitable drive motor 11. The whole pressure filter is disposed onan appropriate stand 4.

As FIGS. 1 and 2 further show, each backwashing head is provided with aplurality of spring struts 6 extending from the center of thebackwashing head to the radial end portion thereof. The spring struts 6extend between brackets 37 which are fastened at the edge of eachcarrier plate 5 and a support block 38 centrally located at therespective carrier plate, wherein the spring struts are clamped betweenthe central support block 38 and the corresponding brackets 37. Thespring struts 6 are biased and apply a corresponding force to thebracket 37 so that a momentum is applied to the radially outer edgeportion of the corresponding carrier plate 5 which pushes this edgeportion of the carrier plate towards the corresponding filter surface.

FIG. 2 shows that each arm of the carrier plate 5 is associated with twospring struts which extend over the corresponding hollow slats. Thespring struts provide that the curved hollow slats with thecorresponding curved slot-like aperture are pressed uniformly againstthe filter surface everywhere so that the pressure difference necessaryfor the backwashing is maintained.

FIG. 3 shows the exact design of the spring struts 6. One recognizesthat the spring struts have a rod 40 which is provided at one end with apiston-like enlargement 41 sealingly (seal 42) guided in a cylinder 43.A number of cup springs 48 is located within the cylinder. These cupsprings act on the piston-like enlargement 41 and thus on the rod 40with a pressure directed to the left in the figure so that the rod actswith a corresponding pressure on the associated bracket 37 (not shown inFIG. 3). At its end away from the rod 40 the cylinder has a stud 44 witha semispherical end surface which engages into a correspondingly formedsemispherical bearing socket 45. This bearing socket is formed at thecentral support block 38 which is mounted to the carrier plate by meansof a central screw 47. Of course, a plurality of semisphericaldepressions 45 is located at the central support block 38. Thesedepressions receive the corresponding spring strut cylinders. The springstruts can freely rotate relative to the backwashing head by means ofthe ball joint formed in this manner.

The spring struts 6 cooperate with a resilient support for therespective contact members of the backwashing head with the filtersurface. According to the shown embodiment the contact members areformed as hollow slats carried by the carrier plate 5 and having at thelower side thereof a slot-like aperture for carrying out the backwashingprocess. The hollow slats with the corresponding slot-like aperture arecurved.

FIG. 4 shows a cross-section through such a hollow slat. One recognizesthe carrier plate 5 over which the drain portion 7 and under which thesuction portion 8 of the backwashing slat (hollow slat) are disposed.The slot-like aperture 30 located at the lower side of the suctionportion 8 narrows into a suction chamber 35 towards the carrier plate,the suction chamber merging into a drain channel 34 extending to thehollow shaft by means of an aperture 36 within the carrier plate.

A resiliently supported contact plate or oscillation plate 31 istdisposed at the side of the slat adjacent to the filter surface. Theplate 31 is resiliently supported at 32. The resilient support is formedby a silicone cushion. One recognizes that the oscillation plate isguided by means of two lateral guide members 39 such that it can onlymove upwardly and downwardly in the figure. Moreover, the oscillationplate 31 is not mounted to the hollow slat but is held through thecontact with the filter surface.

The radial outer regions of the backwashing slats are pressed againstthe filter surface through the spring struts 6. The silicone bearing 32provides for a uniform pressing since corresponding unevennesses on thefilter surface can be compensated by the resiliency of the oscillationplate 31.

FIG. 5 shows a corresponding section through a hollow slat as FIG. 4,wherein here the upper part of the slat is not shown. This embodimenthas a slightly different design of a resilient support 32 for thecarrier plate or oscillation plate 31. In this case, the resilientsupport consists of two elongated silicone cushions consisting each of asheath 51 in which a silicone gel 50 is disposed. The correspondingsupport cushions are disposed in a recess of the lower part 8 of thebackwashing slat. Also in this case the support causes a certain up anddown movability of the oscillation plate 31 for the compensation ofunevennesses on the filter surface.

FIG. 6 shows a radial section through the edge portion of a carrierplate. According to this embodiment the carrier plate is notcantilevered but has a support roller 50 at its radial end which isrotatably mounted at a fastening element 51 by means of a stud 53. Thefastening element 51 is mounted to the carrier plate 5. The height ofthe support roller 50 can be regulated by means of a screw 52. Uponrotation of the carrier plate the support roller 50 rolls on a raisedring 54 which is disposed at the edge of the perforated plates 12 of theassociated filter element. Also in this embodiment the correspondingbackwashing slat, the lower part of which is shown at 8, is providedwith a resiliently supported oscillation plate 31 contacting theperforated plate 12. The corresponding spring struts (not shown in FIG.6) cooperate with the resiliently supported oscillation plate 31 and theroller 50 in order to guarantee a uniform pressure of the backwashingslats against the filter surface. Accordingly, in this case threepossibilities of adjustment are present (spring struts, resilientsupport of the oscillation plate and support roller) so that a veryexact adjustment of the contact pressure of the backwashing headresults.

I claim:
 1. A pressure filter comprising:a housing defining a fluidcompartment, said housing having a fluid inlet communicating with saidfluid compartment; means forming at least one filter surface in thefluid compartment, said filter surface having a plurality of apertures,one side of the filter surface being restricted by the fluid compartmentand another side of said filter surface being restricted by a filtratecompartment formed in said housing and having a filtrate outlet; abackwashing unit comprising a radially extending backwash head extendingfrom a central support to a radially outer portion of said filtersurface, said backwash unit further including means for rotating thebackwashing head to sweep over the filter surface and sealing a part ofthe filter surface with respect to the fluid compartment, thebackwashing head defining a backwashing compartment having at least onesuction chamber having a slot-like aperture opened to the filter surfaceand having connected thereto a reject drain; and a resiliently actingpressure means associated with the backwashing head for pressing aradial outer portion of the backwashing head axially towards the filtersurface, the pressure means being formed by at least one biased radialspring strut supported centrally at the central support and at a radialend portion of the backwashing head.
 2. The pressure filter according toclaim 1, further comprising means for adjusting the pressure applied bythe pressure means.
 3. The pressure filter according to claim 1, whereina part of the backwashing head contacts the filter surface and isresiliently supported.
 4. The pressure filter according to claim 1,wherein the spring strut is supported radially outside the plane of thebackwashing head.
 5. The pressure filter according to claim 1, whereinthe spring strut is supported radially inside in a part-sphericalbearing socket by means of a part-spherical stud.
 6. The pressure filteraccording to claim 1, wherein the spring strut includes a rod engaginginto a cylinder containing at least one spring and on which a pressureis applied by the spring.
 7. The pressure filter according to claim 1,wherein the backwashing head includes a carrier plate at which at leastone hollow slat sweeping over the filter surface is disposed, the hollowslat having the slot-like aperture, and that the resiliently actingpressure means resiliently presses the radial outer edge of the carrierplate towards the filter surface.
 8. The pressure filter according toclaim 7, wherein at least one bracket is disposed at the radial outeredge of the carrier plate, the pressure means being tensioned againstthe bracket.
 9. The pressure filter according to claim 1, wherein thebackwashing head has a bearing at its radial end portion which slides orrolls on the filter surface.
 10. The pressure filter according to claim9, wherein the bearing includes at least one roller rolling on a raisedring of the filter element.
 11. The pressure filter according to claim10, further comprising means for adjusting a pressure of said at leastone roller against the filter element.
 12. The pressure filter accordingto claim 3 wherein the resilient support of a part of the backwashinghead contacting the filter surface is formed by a resiliently supportedplate at a lower side of the backwashing head.
 13. The pressureaccording to claim 12 wherein the plate is supported by a siliconebearing.
 14. The pressure filter according to claim 13 wherein thesilicone bearing is formed by sheathed silicone gel cushions.
 15. Thepressure filter according to claim 12 wherein the plate is guided onboth sides.